This invention relates generally to pulse tube refrigeration which may be used for a high temperature superconductivity application.
Superconductivity is the phenomenon wherein certain metals, alloys and compounds lose electrical resistance so that they have infinite electrical conductivity. Until recently, superconductivity was observed only at extremely low temperatures just slightly above absolute zero. Maintaining superconductors at such low temperatures is very expensive, typically requiring the use of liquid helium, thus limiting the commercial applications for this technology.
Recently a number of materials have been discovered which exhibit superconductivity at higher temperatures, such as in the range from 15 to 75 K. While such materials may be kept at their superconducting temperatures using liquid helium or very cold helium vapor, such a refrigeration scheme is quite costly. Unfortunately liquid nitrogen, a relatively low cost way to provide cryogenic refrigeration, cannot effectively provide refrigeration to get down to the superconducting temperatures of most high temperature superconductors.
An electric transmission cable made of high temperature superconducting materials offers significant benefits for the transmission of large amounts of electricity with very little loss. High temperature superconducting material performance generally improves roughly an order of magnitude at temperatures of about 30 to 60 K from that at temperatures around 80 K which is achieved using liquid nitrogen.
A recent significant advancement in the field of generating refrigeration is the pulse tube system wherein pulse energy is converted to refrigeration using an oscillating gas. Such refrigeration could be used for high temperature superconductivity applications. However, it is presently quite costly to generate refrigeration for use at the more efficient high temperature superconductivity temperatures using known pulse tube systems thus negating the performance improvement seen at the lower temperatures.
Accordingly, it is an object of this invention to provide an improved pulse tube refrigeration system which can provide refrigeration at temperatures which are conducive to good high temperature superconductivity performance.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for providing refrigeration for high temperature superconductivity comprising:
(A) generating an oscillating pulse tube working gas, and cooling the oscillating pulse tube working gas to a first stage temperature within the range of from 50 to 150 K;
(B) cooling the oscillating pulse tube working gas to a second stage temperature within the range of from 4 to 70 K by direct heat exchange with cold regenerator media to produce cold pulse tube gas;
(C) expanding the cold pulse tube working gas in a pulse tube to generate refrigeration for cooling regenerator media; and
(D) providing refrigeration from the cold pulse tube working gas for high temperature super-conductivity.
Another aspect of the invention is:
Apparatus for providing refrigeration for high temperature superconductivity comprising:
(A) a pulse generator for generating oscillating pulse tube working gas, a first stage heat exchanger, means for passing oscillating pulse tube working gas to the first stage heat exchanger, and means for passing refrigeration to the first stage heat exchanger;
(B) a regenerator and means for passing oscillating pulse tube working gas to the regenerator;
(C) a pulse tube in flow communication with the regenerator, said flow communication including a second stage heat exchanger; and
(D) means for providing high temperature superconductivity media to the second stage heat exchanger.
As used herein the term xe2x80x9cpulsexe2x80x9d means energy which causes a mass of gas to go through sequentially high and low pressure levels in a cyclic manner, i.e. to oscillate.
As used herein the term xe2x80x9chigh temperature superconductivity mediaxe2x80x9d means fluid or other heat transfer media which directly or indirectly provides refrigeration to high temperature superconductor material.
As used herein the term xe2x80x9cregeneratorxe2x80x9d means a thermal device in the form of porous distributed mass or media, such as spheres, stacked screens, perforated metal sheets and the like, with good thermal capacity to cool incoming warm gas and warm returning cold gas via direct heat transfer with the porous distributed mass.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cdirect heat exchangexe2x80x9d means the transfer of refrigeration through contact of cooling and heating entities.